1. Field of the Invention
The present invention relates to a processing method of a wafer in which a wafer such as a semiconductor wafer is divided to obtain a plurality of devices, and more particularly, to a processing method in which a wafer has a device region formed with a plurality of devices and an outer peripheral surplus region formed around the device region, and only the device region is thinned and then, the wafer is divided into devices.
2. Description of the Related Arts
Semiconductor chips of devices used for various electronic equipment are produced by a method in which rectangular lattice regions are defined on a surface of a disk-like semiconductor wafer by division lines called streets, electronic circuits are formed on front surfaces of these regions, back surfaces thereof are ground to thin the surfaces, and the wafer is divided along the streets. The slimmed-down tendency of recent years is remarkable and with this tendency, thinner semiconductor chips are required, and this necessitates thinner semiconductor wafers as compared with conventional semiconductor wafers.
If the semiconductor wafer is thinned, however, its rigidity is deteriorated, and there is a problem that it becomes difficult to handle the semiconductor wafer and the semiconductor wafer is easily cracked. Hence, only a circular device region on which the semiconductor chip is formed is ground from its back surface, and its peripheral annular outer peripheral surplus region is formed as a relatively thick reinforcing portion so that the above problem caused by the thinning tendency is not generated. In this case, since the back surface is ground, the thick reinforcing portion projects from the back surface. The technique in which only the outer peripheral portion is thinned is disclosed in Japanese Patent Application Laid-open No. H5-121384 for example.
The semiconductor wafer is finally cut by a cutting apparatus and is divided into semiconductor chips. There is a cutting apparatus of such a type that a semiconductor wafer is absorbed and held on a vacuum chuck type horizontal chuck table, and the semiconductor wafer is cut with a cutting blade from above. The semiconductor wafer is usually supported by a frame mounted on a dicing tape mounted on its back surface, and is held such that its dicing tape side is opposed to the chuck table.
Here, if the semiconductor wafer is a flat plate, its entire back surface comes into intimate contact with the chuck table and thus the back surface is stably held, but if the semiconductor wafer has a thick reinforcing portion projecting toward the back surface of the outer peripheral portion as described above, it is difficult to stably hold the semiconductor wafer. Thus, it is necessary to change the shape of the chuck table such that the chuck table is fitted to the back surface of the concave semiconductor wafer or to grind the reinforcing portion and to form the entire semiconductor wafer into the flat plate shape so that the semiconductor wafer is stably held by the chuck table. However, these methods require much labor and they deteriorate the productivity.